Thermoplastic shrink bands have been in the marketplace for over 20 years. Such bands have been made either in the form of a continuous tube or as a continuous flat film which is seamed to form a continuous tube which is subsequently cut into desired lengths.
Shrink bands can be transparent, or colored, or printed and used primarily as neck or cap seals for tamper-evidence, or are used as labels if they contain printed material. The use of labels has been common on glass or plastic containers, but labels have been very seldom used on metal cans because of costs.
Heretofore, the most common material used for shrink bands has been polyvinyl chloride (P.V.C.). Other materials which can be used, but are less common, are polyester, polyethylene terephthlate (P.E.T.), polystyrene and polypropylene.
In the container art, particularly in the metal can industry, one way of reducing costs has been to make the cans of thinner metal. The limiting factor is, however, the strength of the can. After a can is filled with a product, such as a beverage or food product, it goes into a can seamer that applies a metal end and seams it to the top or open end of the can. In order to get a good seal, the can seamer must exert a great deal of downward pressure on the can end and top of the can. This downward pressure, which is tropically in excess of 100 pounds and may be 200 pounds or more, causes a weak or thin walled can to collapse or buckle. The collapse of a single can in a high production assembly line can cause a large expenditure of time and money incident to stoppage of the line and the requisite clean-up effort. Thus, it is essential that each can has sufficient strength, known as its "axial strength", to withstand the maximum downward, or axial, pressure which is to be encountered.
U.S. Pat. No. 3,542,229 teaches the use of a shrink band of stretchable heat-shrinkable plastic film for increasing the burst strength of a thermoplastic bottle, and teaches the use of a plurality of bands.
U.S. Pat. No. 3,754,699 teaches that a container may be reinforced adjacent the closure receiving flange by using a narrow band as is best shown in FIG. 2.
U.S. Pat. No. 4,007,246 teaches reinforcement of the neck and shoulder portion of a bottle and differential reinforcement of the bottle with the greatest reinforcement being in the neck and shoulder area. There is no teaching or suggestion of reinforcement of the bottle in an axial direction.
U.S. Pat. No. 3,698,586 teaches the expedient of applying a shrinkable sheet around the shoulder area of a bottle.
The above-mentioned patents relate to reinforcement of plastic and glass bottles. U.S. Pat. Nos. 2,810,492 and 3,072,517 teach that a metal can or drum may be reinforced by winding a plurality of layers of paper around the outer periphery thereof. While the first patent makes specific reference to drums, it is noted that in the embodiment of FIG. 2, a closure 31 is applied by using a band 32 which is double seamed to the body. The second patent, i.e., U.S. Pat. No. 3,072,517, discusses axial reinforcement but it is to be noted that the wound paper sheath 12 is incorporated in a double seam as shown in FIG. 3.
The prior art discussed above does not teach or suggest a solution to the problem of axial collapse of a can body during the seaming of a can end onto the can body, and particularly a can body which is necked-in adjacent the closure receiving end.